Make a bookmarklet out of this:
javascript:var%20url=prompt%28%27URL%20of%20the%20document%20to%20upload:%27,location.href%29;if%28url%29location.href=%27http://docs.google.com/?action=updoc&formsubmitted=true&uploadURL=%27%20encodeURIComponent%28url%29;

Add it to your bookmarks bar, and paste in the URL of what you want to add. It defaults to the page you're on, but there may be a way to edit it to default it to what's in the clipboard. My javascript powers are lacking.